Along with miniaturization of a semiconductor device, the trend is moving into a shorter wavelength of the exposure light source and a higher numerical aperture (higher NA) of the projection lens, and a so-called immersion method of filling a high refractive-index liquid (hereinafter sometimes referred to as an “immersion liquid”) between the projection lens and the sample with an attempt to raise the resolution by more shortening the wavelength is known. The immersion method is effective for all pattern profiles and furthermore, can be combined with the super-resolution technology under study at present, such as phase-shift method and modified illumination method.
Since the advent of a resist for KrF excimer laser (248 nm), an image forming method called chemical amplification is used as an image forming method for a resist so as to compensate for sensitivity reduction caused by light absorption. For example, the image forming method by positive chemical amplification is an image forming method of decomposing an acid generator in the exposed area upon exposure to produce an acid, converting an alkali-insoluble group into an alkali-soluble group by using the generated acid as a reaction catalyst in the baking after exposure (PEB: Post Exposure Bake), and removing the exposed area by alkali development.
In recent years, the resist pattern is becoming finer and finer and demands for high resolution are more increasing. In turn, enhancement of various lithography characteristics are required also of the resist composition. Furthermore, for forming various device circuits, a resist capable of forming a resist pattern more faithful to a mask under various conditions is demanded. Such characteristics include pitch dependency and coverage dependency.
In this respect, the resin described in JP-A-2008-111103 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) exhibits high transparency to ArF excimer laser but is insufficient in view of pitch dependency and coverage dependency (the “pitch dependency” indicates the CD (critical dimension, limiting (minimum) dimension) fluctuation of line width of a line-and-space pattern of a resist when the pitch is varied, and the “coverage dependency” indicates the CD fluctuation of line width of a line-and-space pattern of a resist when the reticle mask coverage within an exposure chip is varied).
Also, it is pointed out that when a chemical amplification resist is applied to immersion exposure, the resist layer comes into contact with the immersion liquid at the exposure, as a result, the resist layer deteriorates or a component adversely affecting the immersion liquid bleeds out from the resist layer.
Furthermore, in the immersion exposure process, when the exposure is performed using a scanning-type immersion exposure machine, unless the immersion liquid moves following the movement of lens, the exposure speed decreases and this may affect the productivity. In the case where the immersion liquid is water, the resist film is preferably hydrophobic because of good followability of water.
To solve the problem above, in JP-A-2007-304537 and JP-A-2005-258438, there is described an example of preventing the bleed-out by adding a resin containing a silicon atom or a fluorine atom.
However, combinations of the resin and the fluorine-containing protective film material described in JP-A-2007-304537 and JP-A-2005-258438 are insufficient in terms of pitch dependency and coverage dependency.